使用迭代优化HashMap

Question

我有一个ResultSet包含300K记录,我正在执行以下操作来迭代它(以及其他操作一旦收集).此过程大约需要2分钟才能完成.有没有办法优化它？

Map<String,Map<String,String>> internalMap  = new HashMap<String,Map<String,String>>(); 

while (resultSet.next()) {
    final Integer val1 = resultSet.getInt("val1");
    final String val2 = resultSet.getString("val2");
    final String val3 = resultSet.getString("val3");
    final String val4 = resultSet.getString("val4");
    final String type = resultSet.getString("type");
    final String id = resultSet.getString("id");

    addIntern(internalMap,val2,val1,val3,val4,type,id);
}

以及addIntern上面引用的方法

private static void addIntern(Map<String,Map<String,String>> internalMap, String val2, Integer val1,
    String val3,String val4,String type,String id) {
    String key = id+"##"+val4;
    if (internalMap.get(key) == null) {
        internalMap.put(key, new HashMap<String,String>());
    }
    internalMap.get(key).put("val3", val3);
    internalMap.get(key).put("val2", val2);


    if("create".equals(type)){
        internalMap.get(key).put("create", val1.toString());
    }
    if("update".equals(type)){
        internalMap.get(key).put("update", val1.toString());
    }
    if("delete".equals(type)){
        internalMap.get(key).put("delete", val1.toString());
    }
}

Answer 1

调整你的获取大小resultSet;

resultSet.setFetchSize(100);

你当然可以简化你的添加方法(每个get都是一个O(1)调用,但是它们加起来),就像

private static void addIntern(Map<String, Map<String, String>> internalMap, String val2, Integer val1, String val3,
        String val4, String type, String id) {
    String key = id + "##" + val4;
    Map<String, String> kMap;
    if (internalMap.containsKey(key)) {
        kMap = internalMap.get(key);
    } else {
        kMap = new HashMap<>();
        internalMap.put(key, kMap);
    }
    kMap.put("val3", val3);
    kMap.put("val2", val2);
    if ("create".equals(type) || "update".equals(type) || "delete".equals(type)) {
        kMap.put(type, val1.toString());
    }
}